This invention relates to a method and apparatus for reducing noise in electronic devices that receive or amplify signals, and more specifically, for reducing noise during pauses from an electronic device providing a human voice or other information.
Devices for reducing noise levels are generally known. One such device is disclosed in U.S. Pat. No. 4,703,507. This device includes a circuit that reduces noise during pauses in human voice. Included with this device is a detector that senses a syllable envelope within the audio signal. In response to the sensed audio signal, a DC balance control circuit in the device passes a DC signal to a differential amplifier. The amplifier controls the noise in the audio signal with a DC control.
However, as the noise level at the device's input changes, the DC balance control circuit must be readjusted to cancel the noise. When the noise level changes every two to three seconds, it is not possible to keep the DC balance control level adjusted.
A further drawback to this prior device is that noise may have the same general envelope shape as the syllable. When this noise is received, it will pass directly through the filter causing the noise to appear at the output of the device.